Not Applicable
Not Applicable
1. Field of the Invention
This invention is related to a fuel cell, in particular to a hydrogen fuel cell having a uniform compression device that constantly applies a consistent and distributed operative contact pressure towards a cell stack for enhancing the conductivity and operative efficiency of the fuel cell.
2. Description of the Related Art
With the rapid growth of human civilization the consumption of traditional energy sources, such as coal, oil and natural gas, increases rapidly. This results in serious pollution to the global environment and causes various environmental problems such as global warming and acid rain. It is now recognized that the existing natural energy resources are limited. Therefore, if the present rate of energy consumption continues, all existing natural energy sources will be exhausted in the near future. Accordingly, many developed countries are dedicated to the research and development of new and alternative energy sources. The fuel cell is one of the most important and reasonably priced energy sources. Compared with traditional internal combustion engines, the fuel cell has many advantages such as high energy conversion efficiency, clean exhaust, low noise, and no consumption of traditional gasoline.
In brief, a fuel cell is an electrical power generation device powered by the electrochemical reaction of hydrogen and oxygen. Basically, the reaction is a reverse reaction of the electrolysis of water, to convert the chemical energy into electrical energy. The basic structure of a fuel cell, for example, a proton exchange membrane fuel cell, comprises a plurality of cell units. Each cell unit comprises a proton exchange membrane (PEM) at the middle, with the two sides thereof provided with a layer of catalyst, each of the two outsides of the catalyst is further provided with a gas diffusion layer (GDL). An anode plate and a cathode plate are further provided at the outermost sides adjacent to the GDL. After combining all the above elements together, a cell unit is formed.
For the practical application of a fuel cell, a plurality of the above cell units are stacked and serially connected to provide sufficient power to construct a cell stack, as illustrated in FIG. 1. The cell stack 10 is positioned between two end plates 12, 13 provided at the longitudinal, opposing ends of the cell stack. A tightening device, such as a plurality of tie rods 14, passes through a peripheral region of each end plate 12, 13 for positioning the cell stack 10 between the two end plates 12, 13.
While performing the aforesaid reverse reaction of the electro-dissociation of water, in order to convert the chemical energy into electrical energy, the cell stack must be maintained under a consistent pressure range so as to ensure that the reverse reaction of the electro-dissociation of water is performed under the optimum pressure condition, so as to enhance the conversion efficiency of the chemical energy into electrical energy.
FIG. 2 illustrates a conventional fuel cell, comprising the aforesaid fuel stack 10, two end plates, 12, 13, and a plurality of tie rods 14. Such a conventional fuel cell further includes a plurality of resilient members 50, such as springs, that are affixed between the lower end plate 13 and each of the tie rods 14. Adjustment can be made as to how tight each of the tie rods 14 should be affixed to the end plates, to such a degree that the rebounding force of each of the resilient member 50 being applied to the lower end plate 13 is approximately equal to the contact pressure required for optimizing the conductivity of each cell unit.
Obviously, the object of such a conventional measure for maintaining the pressure is achieved by adjusting the pressure being applied to the lower end plate 13 where each of the resilient members 50 is located. Hence, such a conventional measure can only ensure that the operative pressure neighboring the resilient member 50 can be maintained within a required range, while failing to effectively control the operative pressure at locations remote from the resilient members (or the tie rods 14).
Furthermore, while tightening the tie rods, in order to ensure that each cell unit is under a consistent pressure, precise measurements must be made to each of the tie rods 14 during the tightening process, which complicates the process and increases the cost for manufacturing the fuel cell.
The primary objective of this invention is to overcome the disadvantages of the conventional pressure-maintaining device and to provide a uniform compression device that is able to constantly apply a consistent pressure towards a cell stack. Further, such a uniform compression device can be adapted to adjust the pressure variation caused by thermal expansion, and to compensate for the height deviation resulting from stacking the cell units into a cell stack, thereby enhancing the operative efficiency of the fuel cell.
The major technical content of this invention is to implement a metallic pressure bellows that is positioned between the cell stack and one of the end plates. Because the pressure bellows is made of metal materials, the tendency of pressure leakage is reduced. Further, the pressure bellows constantly applies pressure to the cell stack in a xe2x80x9cplanarxe2x80x9d manner such that the complicated processes required adjusting the conventional pressure maintaining device can be eliminated. The pressure bellows further prevent the pressure being applied to the cell stack from varying with respect to the locations of the tie rods.
The structures and characteristics of this invention can be realized by referring to the appended drawings and explanations of the preferred embodiments.